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Stellar classification
The Harvard Stellar Classification System is used to identify stars based on their color and temperature. Classification Classification } |float = } }} }|text=Hertzsprung–Russell Diagram}} }|text=Spectral Type}} }|text=Brown dwarfs}} }|text=White dwarfs}} }|text=Red dwarfs}} }|text=Subdwarfs}} }|text=Main sequence ("dwarfs")}} }|text=[[Subgiant|Subgiants]]}} }|text=Giants}} }|text=Bright Giants}} }|text=[[Supergiant|Supergiants]]}} }|text=[[Hypergiant|Hypergiants]]}} }|text=absolute}} }|text=magni-}} }|text=tude}} }|text=(MV)}} Class O Class O stars are very luminous and hot supergiant stars, with temperatures as high as 40,000 K. Examples include: *Zeta Orionis *Zeta Puppis Class B *Class B stars are amongst the blue giant and small and middle sized supergiant stars. Their spectra has neutral helium, which are most prominent at class B. These stars have a lifetime of a few hundred to a few million years and if they have mass high enough, they can explode in a strong supernova into an enormous black hole. Examples include: *Rigel (blue supergiant) * Spica (blue giant) Class A Class A are large giants and near-supergiants. These live for about a billlion years and explode as a large planetary nebula and collapse into a dense white dwarf. Examples include: * Sirius (white giant) * Vega (white giant) Class F Class F stars are some of the most common visible stars. These are large enough to explode in a planetary nebula and leave a white dwarf behind. These stars live for up to about a few billion years. Examples include: *Procyon (subgiant) * Canopus (supergiant) *Polaris (supergiant) Class G Class G stars are known as yellow dwarfs and have a temperature between 5,200 K and 6,000 K. These are some of the most common visible stars and they have a very long lifetime of around 10 billion years. They also collapse in a large planetary nebula and leave a dense white dwarf behind. Examples include: *Sol (G2V) *Alpha Centauri A (G2V) * Kepler 22 (G5) * Megaladon (G5) Class K Class K stars are cooler stars which are either orange supergiants, orange giants or orange dwarfs. This spectral type is safe for supergiant stars. Examples include: *Alpha Centauri B (orange dwarf) *Pollux (orange giant) *Arcturus (red supergiant) Class M Class M-stars are by far the most common stars. Most class M-type stars are red dwarfs, but large amounts are red giants and red supergiants. Most of these stars can live up from a billion to 100 billion years. Red supergiants and even hypergiants are stable here. Examples include: *Proxima Centauri (red dwarf) * Betelgeuse (red supergiant) *VY Canis Majoris (red hypergiant) Other classes Class W Class W stars are known more scientifically as Wolf-Rayet stars. They are highly luminous, massive and have helium instead of hydrogen in their atmospheres. They are dying supergiants and hypergiants, with their hydrogen shells blown away by extremely strong stellar winds. Wolf-Rayet related O and B-type stars These stars are inbetween ordinary O and B-type stars and normal Wolf-Rayets. They are still very hot and massive. SLASH stars SLASH-type stars are hot and have a slash in their spectra. Sub-stellar objects There are many objects which are not hot enough at their cores to fuse hydrogen into helium. These are not stars but sub-stellar objects. They can be planets, white dwarfs and brown dwarfs. Brown dwarfs Brown dwarfs are planet-sized, warm, sub-stellar objects, which are not hot enough at their cores to fuse hydrogen-1 into helium. These can actually be mistaken as planets if seen through a telescope. These sub-stellar objects are between the gas giant planets and red dwarfs in mass. L-type brown dwarfs L-type brown are very hot, but still cool brown dwarfs. T-type methane dwarfs Slightly cooler than L-types, the methane dwarfs have a temperature between 700 and 1,300 K. Methane is prominent in their spectra. Y-type ultra-cool dwarfs This is the coldest type of brown dwarf. Those stars have temperatures lower than 700 Kelvins. Around 600,000 ultra-cool dwarfs exist in the Milky Way galaxy. The coldest dwarf has a temperature of around 303 K (27°C). Planets Since planets are not hot enough to fuse hydrogen-1 into helium and do not emit any visible radiation, they are not placed in the Harvard classification system. .